A gas turbine engine is comprised of an inlet, a compressor, a combustor, a turbine, and an exhaust. An annular flow path extends axially from the inlet through the exhaust and is defined by a stator assembly circumscribing a rotor assembly. Air entering through the inlet is pressurized in the compressor, then mixed with fuel and ignited in the combustor resulting in a hot, high pressure gas. The hot gas is expanded across the turbine to produce useful work. A portion of this work is used to drive the compressor and the remainder is used to propel an aircraft with thrust or to drive a free turbine.
The stator assembly has an outer case which contains the working gas and has arrays of stator vanes. Each array of stator vanes extends radially from an outer endwall to an inner endwall crossing the flow path of the working gas upstream of an associated array of rotor blades. The stator vanes direct the working gas into the arrays of rotor blades at angles which optimize the performance of the engine. The stator assembly includes a front and rear bearing support for rotatably supporting the rotor assembly.
The rotor assembly extends axially through the engine and transfers work from the turbine to the compressor. The rotor assembly is comprised of compressor rotor disks and turbine rotor disks. The compressor and turbine rotor disks each have a shaft portion extending axially from the center of each disk. All the shafts are interconnected in series by interstage couplings. Each of the shafts has a hollow center defining a bore extending axially through the rotor assembly. Through this bore cooling air can be passed from the compressor to the turbine. A tie shaft extends axially through the bore. The compressor and turbine disks are mounted on the tie shaft forming a single rotating unit called a spool. The spool is supported by the front and rear bearing supports mounted to the stator assembly. The compressor and turbine rotor disks each have an array of rotor blades radially extending from the disks into the flow path. In the compressor, the rotor blades are angled with respect to the approaching air so as to inject energy and pressurize the air, and in the turbine, the rotor blades are angled with respect to the approaching flow of hot gas to extract work from the gas and convert this work into mechanical energy for driving the turbine disks, shafts, and compressor disks about their axis of rotation.
The interstage coupling is a torque transmitting coupling which may generally be described as having a plurality of radial splines on opposing mating sections that interengage to connect the sections. A problem with these couplings is that the air within the bore radially leaks through the gaps between the meshing radial splines. One approach to reducing the leakage through these gaps is to place a ring seal, as shown in FIG. 2b, between the mating sections of the coupling so that when the mating sections are pressed together, the axial compression forces the seal ring into a sealing engagement with the underside of the radial splines.
Problems with these ring seals have arisen during the assembly of the gas turbine engine. It is common practice, for gas turbine manufacturers, to preassemble the individual components of the gas turbine engine, (e.g. compressor disks, turbine disks, including attaching the mating sections of the interstage couplings to their respective components), separately from each other and then bring all the components together for the final assembly. During the final assembly, the components are mounted vertically. Each component, one by one, is slid over the tie shaft and their respective coupling sections are interengaged. It is during this stacking of the components that the ring seal is manually inserted between mating sections. Because the ring seal is not attached to its mating section prior to final assembly, it is not uncommon for the seal to be inadvertently left out, or for a seal with an improper number of cooling holes to be inserted, or for a seal to be inserted between a set of mating sections where none is required. Any of these assembly errors may result in one or more components of the gas turbine engine not receiving the proper cooling flow which will eventually cause damage to the component(s).
Accordingly, a need exists for an interstage coupling seal and method that can be fixedly mounted to a section of a the coupling prior to the final assembly of the gas turbine engine.